Numerous embodiments of check valves or butterfly valves are already known in which the throughput is controlled by means of a discoidal body fitted in a conduit portion, and mounted on a rotary shaft, allowing it to be displaced by pivoting between a closed position in which it totally blocks and obstructs the passage (a position which is generally perpendicular to the flow direction) and an open position, perpendicular to the previous position and in which it opposes a minimum resistance to the flow of liquid.
Such embodiments of valves or flaps are in particular described in the French patent application No. 00 02644 and in the patent application PCT No. WO 01/16473 in the name of the Applicant.
However, in these known control devices, the evolution of the throughput as a function of the opening (in other words the pivoting) of the valve body is always identical (substantially proportional), as the shape of said body is inevitably adapted to the section of the conduit—to enable closure thereof in the closing position.
However, in certain applications, it may be desirable to have an evolution which is different therefrom flowing from the variable interstice formed between the rotary body and the internal face of the wall.
Thus in certain systems for controlling the throughput, when the flap is opened, the evolution of the liquid passage section can take place too quickly for certain applications which need a wide useful range of throughput at the start of opening.
In this case it would be necessary to reconcile a flap with a large section for large throughputs with full opening and a flap with a small section for small throughputs with a small opening.